Effect of pulp surfaces on enzyme-aided bleaching of kraft pulps

The effects of fibre surfaces on pulp bleachability and on enzyme-aided bleaching were studied by bleaching pine and birch kraft pulps, fibres [i.e. pulps with fines (<100 μm) removed] and mechanically peeled fibres with one stage of hydrogen peroxide treatment. The removal of the primary fines from the pulps resulted in a higher brightness after bleaching. The removal of the outer surface of the pine kraft fibres decreased the brightness after bleaching, whereas no effect was observed with the birch kraft fibres. The xylanase treatment increased the bleachability of both types of pulps, fibres and mechanically peeled fibres, suggesting that its effect on bleaching is not only a surface effect but a broader phenomenon. In the mannanase-aided bleaching of the pine kraft pulp, the presence of the outer surface of the fibres hindered the enzymatic bleach-boosting effect. A positive effect of mannanase on the bleachability of the pine kraft pulp was observed only after the removal of the outer surface of the fibres